The present invention relates to an alignment disk for use in adjustment of the position of or inspection of a magnetic head of a floppy disk drive unit.
A floppy disk drive unit has two magnetic head assemblies on opposite sides of the disk for writing data in and reading data from the respective sides of the floppy disk.
Data is recorded along tracks extending circumferentially. The intervals between adjacent tracks are designed to be smaller and smaller to meet the demand for higher data storage capacity.
As an example, a typical track-to-track interval was 529 micrometers, whereas a narrower interval of 265 micrometers is now more often employed. The future trend is toward even narrower intervals. Accordingly, higher precision is required for the adjustment of the ralative position between the two magnetic head assemblies, and for the positioning of the two assemblies relative to the frame of the disk drive.
Use of an alignment disk for the adjustment is often adopted. A problem associated with the use of an alignment disk is a waveform interference due to magnetic coupling between an erase head and a read/write head.
To solve the problem, Japanese Patent Application Publication No. 39443/1982 proposes that a certain frequency should be used for the signal recorded on the alignment disk. When this teaching is followed in connection with a 5-inch floppy disk with inter-track distance of 529 micrometers, a suitable range of the frequency f is given as follows: With the distance from the axis of rotation of the disk to the position of the head: r 32 46563 micrometer, with the rotational speed of the disk: n=5 (rps), with the minimum (within the tolerance) inter-head (gap) distance: L.sub.RE(MIN) =800 micrometers, with the maximum (within the tolerance) interhead (gap) distance: L.sub.RE(MAX) =900 micrometers, and with the minimum inter-magnetic-transition distance:a=10 micrometers, the following relationship must be satisfied. EQU 925.84 m&lt;f&lt;803.74 (m+1),
where m is 0 or a positive integer. The above relationship is satisfied if m.ltoreq.6. The maximum frequency is therefore EQU 803.74.times.(6+1)=5626 HZ.
This value is substantially lower compared with the frequency 125 kHz, which is the frequency of the signals used in the conventional alignment disk. With such a low frequency, the waveform of the signals which appear on an oscilloscope is faint and is difficult to observe.
If the brightness is increased by increasing the gain of the oscilloscope, the base line becomes too bright and is tiring to the obserbing person's eyes. These problems are particularly serious where the oscilloscope is used in a mass production line, for the adjustment or inspection of mass-produced floppy disk drive units.